Navigate to your rgl_config.txt folder which should be in C:\Users\YourUsername\Documents\Mount&Blade Warband\ and see if it has both of these two:
use_secure_connection = 0
max_number_of_connections = 16
If both of those are correct, try playing around with the max_number_of_connections number to see if that fixes it. Also, try resetting your router and modem to see if that fixes it.